Comparative structural profiling of trichome specialized metabolites in tomato (Solanum lycopersicum) and S. habrochaites: acylsugar profiles revealed by UHPLC/MS and NMR

Abstract

Many plants accumulate large quantities of specialized metabolites in secretory glandular trichomes (SGTs), which are specialized epidermal cells. In the genus Solanum, SGTs store a diverse collection of glucose and sucrose esters. Profiling of extracts from two accessions (LA1777 and LA1392) of Solanum habrochaites using ultra-high performance liquid chromatography–mass spectrometry (UHPLC/MS) revealed wide acylsugar diversity, with up to 11 isomers annotated for each individual elemental formula. These isomers arise from differences in ester chain lengths and their positions of substitution or branching. Since fragment ion masses were not sufficient to distinguish all isomers, 24 acylsucroses were purified from S. habrochaites accessions and cultivated tomato (Solanum lycopersicum M82) and characterized using NMR spectroscopy. Two-dimensional NMR spectra yielded assignments of positions of substitution of specific acyl groups, and locations of branching. The range of substitution was wider than reported earlier, and in contrast to previous reports, tetra- and penta-acylsucroses were substituted at position 2 with acyl groups other than acetate. Because UHPLC/MS fails to yield sufficient information about structure diversity, and quantitative NMR of acylsugar mixtures is confounded by structural redundancy, the strategic combination of NMR and UHPLC/MS provides a powerful approach for profiling a class of metabolites with great structural diversity across genotypes.Electronic supplementary materialThe online version of this article (doi:10.1007/s11306-013-0585-y) contains supplementary material, which is available to authorized users.

In vitro reconstruction and analysis of evolutionary variation of the tomato acylsucrose metabolic network

“…Cultivated tomato produces primarily tri-and tetraacylated sucrose esters in the tip cell of the long multicellular "type I/IV" trichomes (14,29). Although two trichome apical cell-expressed BAHD acyltransferases that produce tri-and tetraacylsucroses from diacylsucroses were recently described (25,29), the enzymes that convert sucrose to diacylated sucrose have not been previously reported.…”

“…Acylsugar phenotypic diversity was observed for various wild tomato species and for accessions within S. pennellii and S. habrochaites (14,(24)(25)(26). For example, we recently demonstrated that introgression of a region of S. pennellii LA0716 from the top of chromosome 8 (IL8-1-1) causes increased accumulation of iC4-containing acylsucroses due to introduction of a gene encoding a truncated Leu feedback-insensitive isopropylmalate synthase (IPMS)-like enzyme (Sp-IPMS3) (15,26).…”

“…Protective properties against herbivores have made increasing total acylsugars or altering acyl chain types a target for breeding insect-resistant cultivated tomatoes (Solanum lycopersicum) (16-18). In addition, synthetic sucrose esters mimicking natural acylsugars have been applied as safe, biodegradable insecticidal compounds (19-21) and also have commercial value in the food, cosmetic, and pharmaceutical industries (22,23).Recent work on acylsucrose biosynthesis in trichomes of the tomato clade revealed that this relatively closely related group of plants produces a surprisingly diverse group of acylsucroses in tip cells of the long hair-like type I/IV trichomes (14,(24)(25)(26). The genetic and biochemical mechanisms underlying some of this phenotypic diversity have begun to be revealed.…”

“…For example, acylsugars are a group of structurally related specialized metabolites produced in plants of the nightshade family-the Solanaceae (9,10). Characterized examples in the tomato group of Solanum consist of either a glucose or a sucrose backbone with three to four aliphatic acyl groups of varying carbon numbers ranging from 2 to 12 esterified to the sugar hydroxyl groups (11)(12)(13)(14)(15). Nicotiana attenuata acylsucroses are at the center of a multitrophic defense interaction where they are metabolized to volatile fatty acids by Manduca sexta larvae, and these airborne products attract predatory ants (6).…”

“…Recent work on acylsucrose biosynthesis in trichomes of the tomato clade revealed that this relatively closely related group of plants produces a surprisingly diverse group of acylsucroses in tip cells of the long hair-like type I/IV trichomes (14,(24)(25)(26). The genetic and biochemical mechanisms underlying some of this phenotypic diversity have begun to be revealed.…”